Motor racing-Battery problem affected Hamilton's qualifying

BARCELONA, May 11 (Reuters) - Lewis Hamilton's Spanish Grand Prix qualifying was affected by a battery problem, Mercedes principal Toto Wolff said on Saturday after the reigning champion lost out to team mate Valtteri Bottas in the battle for pole position.

Championship leader Bottas beat the Briton, who had been on pole at the Circuit de Catalunya for the past three seasons, by a hefty 0.634 seconds.

"In Q2 (the second phase of the session) on the second lap, there was a yellow (flag) and he aborted the lap and pitted," explained the Austrian.

"Normally you need the cool down lap to recharge the battery, that's why he ended up in the garage with a battery that wasn't full."

Wolff said Hamilton was then sent out early in the final phase, which put him on "the wrong foot" because he came across other slower cars who had just left the pits when it came to doing his flying lap.

"That obviously compromised his lap massively," he added.

Hamilton told reporters he had just not done very good laps, although he was still quick enough to secure a Mercedes front-row lockout for Sunday's race.

Mercedes have had one-two finishes in the first four races of the season and look likely to make it five, providing they avoid any coming together.

Bottas is a point ahead of Hamilton in the championship, thanks to a fastest lap in Australia, and the Briton said after the previous race in Azerbaijan that he had been too nice to the Finn on track.

In 2016, a dominant season for Mercedes with Hamilton fighting an ultimately losing battle with then team mate Nico Rosberg for the title, the two Silver Arrows collided on the opening lap in Spain and retired.

Wolff recognised that was a concern but said the situation was very different now.

"Everybody knows that lap one is very important and in Barcelona can be race-deciding," he said. "But the two have been so respectful with each other, on and off track, that we are in a very different place than we were in 2016.

"We completely acknowledge there is rivalry between the two of them, and that will intensify the longer the championship goes if it is between them," he added.

"We will chat tomorrow morning and talk about scenarios and play a few videos. They know." (Reporting by Alan Baldwin, editing by Ed Osmond)